Alcohol is one olthe most commonly abused drugs in the US, with 10% of the population affected by alcohol dependence at some point in their lives. Research over the last 20 years has demonstrated that individual dIfferences in subjective responses to alcohol may influence a person's pattern of alcohol use and is a strong predictor of future alcoholproblerns. Individuals with a low response to alcohol have an Increased-risk for alcoholism, where as Individuals With a-high response to alcohol have a reduced risk for alcoholism. Mu oploid receptors are involved in modulation of drinking behaviors and have been shown to be higher in recently abstinent alcoholics when compared to healthy controls. The current application furthur investigates the relationships between differences In brain mu opioid receptors and Individual differences In subjective responses to alcohol. We will recruit healthy social drinkers who Will complete an alcohol challenge procedure and be phenotyped based on their level of response to alcohol. Subjects who show a high response and a low response to aIcohol will undergo a [C11] carfentanil PET scan toobtain MOR BP to determine if individual differences in MOR BP are related to alcohol sensitivity under controlled laboratory conditions. The results of the proposed research will increase our understanding of to the relationship between individual variability in the opioid system and subjective sensitivity to alcohol.